1. Field of the Invention
The present invention relates to a method for controlling an air conditioner for a vehicle, in particular, to a method for controlling an air conditioner for a vehicle, which can prevent undershoot of an evaporator by performing a maximum capacity control or controlling a discharge capacity of a compressor through the output of a control value of the discharge capacity of the compressor directly before the stop of the air conditioner, and can improve the pleasant feelings of the passengers by preventing delay of response, which converges into the target temperature of the evaporator due to the delay of the temperature decrease of the evaporator.
2. Background of the Related Art
In general, with regard to a vehicle, especially, a vehicle with an internal combustion engine, which produces power by burning fossil fuel as a power source, has been generalized and mass-produced. Recently, a hybrid vehicle has been developed, which can be operated by the power selectively transferred from a motor or an internal combustion engine due to problems associated with the harmful discharge gas according to the burning of the fossil fuel and the exhaustion of the fossil fuels, and the like.
Such a conventional vehicle is provided with an air conditioner for performing cooling and heating of vehicle indoors. In this regard, in connection with a construction of a cooling system in the air conditioner, a swash type compressor is employed as a compressor for supplying gaseous refrigerant with low temperature and pressure, which is introduced from the evaporator, to a condenser after compressing it into gaseous refrigerant with high temperature and pressure.
The swash type compressor is driven□according to the turning on/off of an air conditioner (A/C) switch. When the compressor is driven, the temperature of the evaporator is decreased, and when the compressor is stopped, the temperature of the evaporator is increased.
Meanwhile, the swash type compressor can be divided into a fixed capacity type compressor and a variable capacity type compressor. Recently, the variable capacity type compressor is mainly used which can vary the discharge capacity.
The variable capacity swash type compressor generally employs a pressure control valve for controlling the discharge capacity of the refrigerant, and may sometimes employ an electronic control valve (ECV) using an electric force in place of the pressure control valve with a mechanical structure.
In other words, in case of the variable capacity swash type compressor employing the ECV, the inclination of the swash can be varied according to duty of the ECV, and the discharge capacity of the refrigerant is determined depending on the inclination of the swash.
As a result, the capacity of the refrigerant supplied to the evaporator is varied according to the duty of the ECV, and this means that the duty value of the evaporator is an important factor for determining the temperature of the evaporator.
In other words, in case of the variable capacity swash type compressor employing the ECV, the inclination of the swash can be varied according to duty of the ECV, and the discharge capacity of the refrigerant is determined depending on the inclination of the swash.
As a result, the duty value of the ECV is calculated by a time during which the ECV is turned on, among the whole operation time of the compressor, by percentage.
Accordingly, when the duty value is high, the discharge capacity of the refrigerant increases, and when the duty value is low, the discharge capacity of the refrigerant decreases.
With regard to the vehicle provided with the air conditioner having a variable capacity swash type compressor, it is necessary to operate the air conditioner according to the deviation of the temperature between the present temperature and the target temperature at the initial time of the operation of the air conditioner.
For instance, while the compressor is preferable to be driven at an discharge capacity which does not produce large noise, it goes without saying that target temperature of the evaporator can be effectively reached and the entrainment feeling is not worsen. In this regard, in Japanese Patent Laid-Open Publication No. 2003-200730, there is disclosed a technology of controlling the discharge capacity of the compressor by a proportional integral, after setting the duty of the ECV of a variable capacity swash type compressor with respect to the deviation between the target temperature of the evaporator and the present temperature.
According to the above technology, when the deviation between the target temperature of the evaporator and the present temperature is above a predetermined value, for instance, 3□, a maximum capacity control is performed, and when the present temperature of the evaporator is lower than the target temperature of the evaporator by at least 3□, a minimum capacity control is performed, so that the temperature control performance such as a temperature convergence, and a response time is dependent upon how a proportional gain and an integral gain are properly selected according to the system, when the proportional integral control is performed by the feed-back of the present temperature of the evaporator with respect to the target temperature of the evaporator.
However, the conventional art technology entails a problem in that the convergence and the pleasantness are degraded when the temperature of the outdoor air is low or the target temperature of the evaporator is high, since there occurs an undershoot phenomenon, in which the temperature of the evaporator drops sharply in case of performing the maximum capacity control at the initial time of the operation of the air conditioner, whereas the temperature of the evaporator become lower than the target temperature of the evaporator for a predetermined time.
Also, the conventional art technology encounters another problem in that the undershoot phenomenon is reduced but the time taken for converging into the target temperature of the evaporator is extended due to the delay of the decrease of the temperature of the evaporator, when the proportional-integral control is performed which is the maximum capacity control and concurrently the minimum capacity control at the initial time of the operation of the air conditioner.